Species succession and the development of a lacustrine fish community in an ephemeral lake

Abstract

Here, we present a gillnet survey of Lake Liambezi a 370 km 2 shallow ephemeral floodplain lake situated in north-eastern Namibia, which is fed irregularly by the upper Zambezi and Kwando Rivers during years of high flooding. The lake dried up in 1985 and, with the exception of sporadic minor annual inundation events, remained dry until 2007. We describe the temporal succession of fish species over an 8 year period from initial inundation 2007 to maturation in 2014. The succession of the fish community did not follow the typical pattern of opportunistic strategists during colonisation, to periodic strategists that are eventually succeeded by equilibrium strategists. Instead, the evolution of the fish community was characterised by three distinct phases. The first phase involved the inundation and colonisation of the lake in 2007, followed by its decline until the floods that filled the lake in 2009. During this phase the lake was colonised by fishes from the adjacent upper Zambezi and Chobe River floodplains. Fish communities predominantly comprised floodplain specialists including the barbs Enteromius paludinosus and Enteromius poechii, the mormyrid Marcusenius altisambesi and catfishes Schilbe intermedius and Clarias gariepinus. The filling of the lake in the March 2009 floods marked the beginning of the second, successional phase. The barbs declined in abundance and the alestid Rhabdalestes maunensis underwent explosive population growth between 2009 and 2010, but populations crashed equally rapidly and were replaced by Brycinus lateralis which, together with S. intermedius went on to dominate the fish community 2011-2014. Larger, slower growing tilapiine cichlids increased steadily in abundance and became the dominant components in a 2700 t y -1 artisanal fishery that developed on the lake. The fish community in the ephemeral Lake Liambezi is clearly influenced by numerous factors including connectivity, lake level

Fish community composition in small lakes: The impact of lake genesis and fisheries management

“…Hence, the impact of lake genesis on β‐diversity, as evidenced from higher β‐diversity in the unmanaged gravel pit lakes relative to the unmanaged natural lakes, probably was caused by differences in lake age. Furthermore, the number of species colonising a lake rises with lake age (Barbour & Brown, 1974; Peel et al, 2019). Hence, the high variation in fish community composition in newly created unmanaged gravel pit lakes most probably resulted from the stochastic colonisation process as evidenced by presence of small‐bodied pioneer species, such as sunbleak and ninespine stickleback (Gozlan et al, 2003; Merilä, 2013; Mobley et al, 2011) and highly variable (among lakes), yet overall species‐poor community composition.…”

Food Web Structure and Trophic Dynamics of a Fish Community in an Ephemeral Floodplain Lake

“…The annual average evaporation rate is as high as 2,500 mm (Mendelsohn and Roberts, 1997). The composition of the Lake Liambezi fish community underwent a series of successional changes from its full inundation in 2007 until 2010, but remained largely the same from 2011 to 2014, suggesting the fish community may have reached maturity (Peel et al, 2019) and comprises 46 species from 10 families ( Supplementary Table 1; Peel et al, 2015).…”

“…While the three trophic pathways discussed above are by no means discrete (fishes may forage across pelagic and benthic food chains), predators occupying the highest trophic levels fully integrate all pathways (Vander Zanden and Vadeboncoeur, 2002). The dominant predator in Lake Liambezi in terms of biomass was S. intermedius ( Supplementary Table 1; Peel et al, 2015Peel et al, , 2019, a generalist predator, which consumed a wide variety of prey items including fish, aquatic and terrestrial invertebrates, decapods and gastropods. The broad, but fish-dominated diet of S. intermedius observed during the present study was consistent with previous observations from Lake Liambezi (van der Waal, 1985) and with dietary (Merron and Mann, 1995;Winemiller and Kelso-Winemiller, 1996) and trophic (Taylor et al, 2017b) assessments in neighboring rivers.…”

“…A combination of dietary overlap, dietary specialization, the integration of multiple food chains and the behavioral adaptation to changing dietary resources, underpins the ability of Lake Liambezi's fish community to thrive under the stochastic nature of ephemeral ecosystems. Unfortunately, the development of a substantial subsistence tilapiine fishery on Lake Liambezi (Peel et al, 2015(Peel et al, , 2019 combined with the recession of lake water after 2014 resulted in the collapse of the cichlid fishery in 2016 (Peel et al, 2019;Tweddle, personal observation). The management of Lake Liambezi during its next cycle of inundation should likely focus on monitoring size and abundance of fish species involved in the longer phytoplankton based pelagic food chain, as its length and complexity would contribute to ecosystem stability.…”

“…The lake reached a peak surface area of around 370 km 2 during successive floods in 2010 and 2011 and remained inundated, despite receiving minimal inflow until 2017. The lake hosts a thriving fish community (Peel et al, 2015(Peel et al, , 2019 and consequently supports an active subsistence fishery, based primarily on large cichlid species, particularly Oreochromis andersonii and Oreochromis macrochir, however, the ephemeral nature of Lake Liambezi also puts it at risk of overfishing (Simasiku et al, 2017). The lake also supports extensive areas of aquatic macrophytes (Seaman et al, 1978;Peel et al, 2015), including vast, fragmented stands of the emergent reeds Phragmites australis (Gramineae) and Typha capensis (Typhaceae), which| provide shelter from wind and wave action, enabling the submerged macrophytes Lagarosiphon ilicifolius (Hydrocharitaceae) and Najas horrida (Hydrocharitaceae) to flourish in shallower areas.…”